There have been numerous studies conducted to determine the frequencies of CTD. These investigations, however, were usually not population based, relied on data sources set up primarily for administrative purposes, lacked unified methodologies for case definitions and verification, and failed to estimate the level of case ascertainment. Population based registries offer an alternative to past approaches and should not be overlooked for CTD. We propose that a standardized approach, as outlined above, will facilitate the development of registries and will permit the evaluation of the incidence of CTD across race, geographic area, and time. The establishment of standardized population based registries would form the foundation of a coordinated national and global effort to identify the etiology, and perhaps preventative measures, for these serious conditions.